As many people getting ready for Monday’s solar eclipse, experts are warning those who are taking in the event to take good care of their eyes.

Several states in the U.S. will see a rare total eclipse, meaning the moon will completely cover the sun. The path of totality will stretch from Salem, Ore. to Chaleston, S.C. The total eclipse will last from 10:16 a.m. PT to 2:48 p.m. ET.

Canadians will see a partial eclipse, with the western coast seeing the most dramatic coverage of the sun.

Wherever you are taking in the spectacle, you should wear protective eyewear or you risk going blind, experts said. Even pets are vulnerable to eye damage from looking at an eclipse, though they don’t tend to look directly at the sun.

Looking directly at the powerful brightness of the sun can cause damage to the retina, the light-sensitive part of the eye. Even the smallest amount of exposure can cause blurry vision or temporary blindness.

Ralph Chou, a University of Waterloo optometry professor and president of the Royal Astronomical Society of Canada, said staring at the sun for more than a few seconds will cause harm.

He said the eye feels no pain so it will be too late to look away from potential retina-burning solar rays before a person notices they’ve done potentially permanent damage.

“The light from the sun is very intense and concentrated into a very small area, and then that light is converted into heat and that heat cooks the retina,” Joel Schuman, chair of ophthalmology at NYU Langone Health, told Vox. “So you have a permanent area that you don’t see, a permanent blind spot.”

Once your retina burns, it is permanently damaged, he added.

What glasses should you have?

NASA released a statement explaining “eclipse viewing glasses” or “handheld solar viewers” must be used. The space agency said solar eclipse glasses should be marked with the “ISO 12312-2” international safety standard on the label, and you should make sure there are no scratches on the lenses.

Those who want to purchase the special glasses can buy them online. The price range varies but begins at just a couple of dollars. However, it’s important the glasses come with the certification.

Amazon recently pulled fake solar eclipse glasses from its website and issued refunds to customers who had already purchased them. In an email to buyers, the company said it could not get confirmation from the supplier that the glasses came from a recommended manufacturer.